Method for purifying septic tank effluent

ABSTRACT

Liquid effluent from a conventional septic tank is passed successively through a filter tank and a plurality of spaced ozonating tanks, at least one of which has an activated charcoal filter located intermediate its ends. The filtered liquid passes from the last ozonating tank into a reservoir, and finally through an overflow outlet to a surrounding leach field. Perforated diffusers in the lower ends of the ozonating tanks are connected to an ozone generator which intermittently supplies ozone gas to the diffusers. Excess ozone gas is piped from the upper ends of the ozonating tanks back to the septic tank to increase the effectiveness of the septic tank. Dimethyl sulfoxide is added to the septic tank to prevent sludge formation.

This application is a continuation-in-part of my copending applicationSer. No. 687,041, filed May 17, 1976, now U.S. Pat. No. 4,104,166,granted Aug. 1, 1978.

The invention relates to waste water treatment, and more particularly toan improved method for purifying septic tank effluent.

Conventional septic tanks produce a liquid effluent which is leachedinto the soil around the tank through a system of drain tile, or thelike. Upon being leached into the soil, anerobic bacteria act upon theeffluent to purify it by the process of digestion. While under idealconditions this process is reasonably effective in removing undesirableodors and bacteria from the effluent, this effectiveness will varyconsiderably depending upon various factors, including the type of soilinto which the effluent is leached, the capacity of the system inrelation to the number of persons utilizing the facilities serviced bythe septic tank, etc.

It has been discovered, however, that the reliability and efficiency ofsuch systems can be enhanced considerably by adding additionalpurification apparatus to clean the septic tank effluent before it isdischarged into a leach field, or the like. Moreover, by employingcertain additives, the breakdown of solid particles can be expedited,thus minimizing undesireable sludge build-up in the system. Also by theaddition of air and oxygen, which is fed into the drain tile from thehereinafter described ozone system, aerobic bacteria digest any sludgein the drain tile, as well as increase the action of aerobic bacteria inthe soil around the drain tile, which prevents the build-up of anundesireable mat in the soil adjacent the tile, and which wouldotherwise, if present, slow up the leaching process.

It is an object of this invention, therefore, to provide an improvedprocess for purifying the effluent of septic tanks, thereby enablingsuch tanks to function reliably and effectively regardless of the natureof the soil into which the effluent is discharged.

Another object of this invention is to provide an improved process forfiltering and ozonating a septic tank effluent before the effluent isleached into the surrounding ground.

Still another object of this invention is to improve the quality of theeffluent from a septic tank system by employing additives which assistin removal of undesirable odors and gases from the effluent, andexpedite the break-down of solid particles in the sewage being treated.

Other objects of the invention will be apparent hereinafter from thespecification and from the recital of the appended claims, particularlywhen read in conjunction with the accompanying drawings.

In the drawings:

FIG. 1 is a schematic view illustrating ozone generating apparatus andcontrols therefor which can be utilized to supply ozone gas topurification apparatus of the type made according to one embodiment ofthis invention;

FIG. 2 is a fragmentrary sectional view taken on a vertical planethrough a purification tank which forms part of the above-notedpurification apparatus, the tank being shown connected to the output oreffluent of a conventional septic tank;

FIG. 3 is an enlarged, fragmentary plan view of this tank with its coverremoved to illustrate the arrangement of several ozonating tankscontained within this purification tank;

FIG. 4 is a fragmentary elevational view illustrating schematically onemanner in which the ozonating tanks of FIG. 3 may be connected to eachother;

FIG. 5 is a fragmentary elevational view of still another way in whichthese ozonating tanks can be connected to provide a counterflow relationbetween the septic tank effluent and the ozone gas employed in thesetanks; and

FIG. 6 is an enlarged, vertical sectional view taken through the centerof a filter unit which is adapted to be employed in this apparatus.

Referring now to the drawings by numerals of reference, and first toFIG. 1, 10 denotes a conventional ozone generator to which compressedair is supplied by an air compressor 11, which has an air inlet filter12 for removing undesirable dust particles, and the like from incomingair. The output of the compressor 11 is dried by a pair of air dryers 13and passes through a pressure regulator 14, a finned cooling pipe 15,and an expansion valve 16, which is located in the input ot the ozonegenerator to effect adiabatic cooling of the incoming air. A fan 17 isalso placed adjacent the pipe 15 to direct cooling air thereover.

The high voltage coil in the generator 10, which is denotedschematically at 18 in FIG. 1, is energized or otherwise controlled by aconventional timer circuit, which is denoted generally at 19. Thecircuit, which forms no part of this invention, may be set to energizethe generator 10 periodically to supply ozone gas to its output line 20.The output of the generator 10 comprises a mixture of ozone gas and air,and is fed by the line 20 to a plurality of ozone tanks of the typedescribed in greater detail hereinafter.

Referring now to FIG. 2, 25 denoted generally a conventional septic tankcontaining a pair of spaced, parallel, transversely extending bafflemembers 26 and 27, the upper edges of which are spaced slightly beneaththe septic tank cover 28, and the lower edges of which are spacedslightly above the bottom 29 of the tank in the usual manner, so thatsewage entering the tank through the waste line 30 must pass beneath thelower ends of the baffles 26 and 27 in order to reach the generallyT-shaped outlet pipe 32, which is secured in the outlet end of tank 25.The horizontally disposed leg 33 of the outlet pipe 32 is located at alevel which is spaced slightly beneath the inlet pipe or waste line 30,so that the level L (broken lines in FIG. 2) of the sewage in tank 25normally will not rise above the outlet leg 33.

The tank cover 28 contains the usual cleaning opening 36 covered by aremovable lid 37 to enable the tank to be pumped out or otherwiseserviced, when necessary. Moreover, if required, the waste line 30,which is connected to the household plumbing or other system serviced bythe tank 25, may be connected by a pipe 38 to a supply of apolyelectrolyte, and by a pipe 39 to a coagulant supply, so that desiredquantities of these materials can be added to the waste prior to itsdischarge into the septic tank. The system, however, will worksatisfactorily without this feature.

Referring now to the embodiment illustrated in FIGS. 2 to 4 and 6, 40denotes a cylindrical purification tank, which is adapted to be placedin the ground adjacent the septic tank 25. A cylindrical filter tank 42of smaller diameter and height than tank 40 is secured at its lower andcoaxially to the bottom of tank 40, and has an open upper end spacedbeneath the cover or lid 43 of tank 40

Removably mounted on a ring or annulus 55 which is secured in tank 42intermediate its ends, is a cylindrical filter unit 44. This unitcomprises a plastic, tubular housing 45 (FIG. 6) having around its lowerend an internal, circumferential flange 46. Seated on this flange acrossthe lower, open end of housing 45 is generally disc-shaped stainlesssteel screen 47. Supported on screen 47 is a layer 48 of peat gravel,which is covered in turn by layer 49 of anthrofil or granulated coal,and a layer 50 of fine sand. Surrounding the upper end of housing 45,and seated in an annular recess in its outer surface, is a resilientO-ring or gasket 51 which has sealing engagement with the innerperipheral surface of tank 42, when the filter unit 44 is mountedtherein as shown in FIGS. 2 and 3. An integral handle 52 is formed onthe upper end of housing 45 to enable the filter unit readily to beinserted into, or withdrawn from, the tank 42.

Mounted in the lower end of tank 42 on the bottom of tank 40, andbeneath the filter 44, is a backwash pump 60, which has an inlet 61communicating with the bore of tank 42 beneath the filter, and an outletconnected by a pipe 63 with the interior of the septic tank 25. Thedischarge end of the pipe 63, it will be noted, is disposed above thelevel of the sewage in tank 25 for purposes noted hereinafter.

Adjacent its lower end, the filter tank 42 is connected by a pipe 65with the outlet pipe 33 of the septic tank 25, so that effluent fromtank 25 is fed into the bottom of the tank 42 beneath the filter 44.Adjacent its upper end tank 42 has an outlet pipe 66, which is connectedthrough a conventional flap valve 67 and an inlet pipe 68 to the upperend of a cylindrical, vertically disposed ozonating tank 71, the lowerend of which is seated on the bottom of tank 40 in the radial spacebetween tanks 40 and 42.

Also seated on the bottom of tank 40 and extending upwardly in theannular space between tanks 40 and 42, and in spaced, parallel relationto one another and to tank 71, are four additional ozonating tanks 72,73, 74 and 75 which are similar in construction to tank 71. The tanks 71to 75 are sealed at their upper ends by identical, removable covers 70;and each contains an ozone supply pipe 76 which projects at its upperend through the associated tank cover 70, and which has on its lower enda perforated, right-angular diffusion section 77, which is spaced justabove the bottom of the associated ozonating tank. At their upper endsthe ozone supply pipes 76 are connected through separate,manually-operable gate valves 78, or the like, with a manifold pipe 79(FIG. 2), which is connected to the ozone supply pipe 20. The valves 78are adjustable to allow ozone gas to pass downwardly through the pipes76, and to be released through the perforations in the diffusingsections 77 so that the ozone gas will bubble upwardly in each tank 71to 75, when the apparatus is in use, as noted hereinafter.

To cause the filtered fluid from the tank 42 to pass successivelythrough the ozonating tanks 71 to 75, the tank 71 is connected adjacentits lower end by a pipe 81 (FIGS. 2 to 4) to the lower end of theadjacent tank 72. Tank 72, at a height corresponding to the water levelL, is connected by a pipe 82 to the upper end of the next adjacent tank73, which, in turn, is connected adjacent its lower end by a pipe 84,with the lower end of the tank 74. At its upper end tank 74 is connectedat a height approximating the water level L by a further pipe 85 to theupper end of the last ozonating tank 75. Adjacent its lower end tank 75has an outlet connected to a vertically disposed discharge pipe 86, theupper end of which opens on the annular space between tanks 40 and 42,and at a level or height equivalent to that of the desired level L ofthe sewage in the system. Consequently, the filtered and ozonated fluidthat is discharged from the pipe 86 is stored in the annular spaceformed between tanks 40 and 42, and around the outsides of the ozonatingtanks 71 to 75. This space constitutes a reservoir for holding effluentafter it has passed through the filtration and ozonating stages of thesystem. Adjacent the upper end of tank 40 an outlet pipe 90 is connectedto an opening in the tank at the level L to allow excess fluid from thereservoir to flow into the leach field (not illustrated) which normallywould be located around the outside of the tanks 25 and 40.

Above the pipes 82 and 85, so as to be located above the level L of thefluid contained in the ozonating tanks, these tanks 71 to 75 areinterconnected by a pipe 91 (FIGS. 2 to 4), which extends between theupper ends of tanks 71 and 72; by a pipe 92, which extends between theupper ends of tanks 72 and 73; by a pipe 93 which extends between theupper ends of tanks 73 and 74, and by pipe 94 which extends between theupper ends of tanks 74 and 75. Tank 75 is also connected at its upperend by a return pipe 95 with a perforated, horizontally disposeddiffusion pipe 96 (FIG. 2), which is located in the septic tank 25 abovethe bottom 29 of the tank, and between the baffles 26 and 27. Thepurpose of pipes 91 to 96 is to allow any foam, and/or excess ozone gas,which may otherwise accumulate in the upper-ends of the ozonating tanks71 to 75, to pass through these tanks and the pipe 95 back to the septictank 25, where the gases can be utilized to improve the effectiveness oftank 25.

In practice, the ozone generator 10 and the associated equipmentillustrated in FIG. 1 may be placed in a separate cabinet in a garage orbasement, or in a weather-proof box placed outside of the building thatis to be serviced by the septic tank 25 and its filtering apparatus. Thegenerator may be of the conventional variety which can be powered by 115volt AC power supply, which may be increased up to 500 cycles, ifnecessary, by menas of a solid state frequency changer (notillustrated). Each upward change in the frequency, of course, increasesthe ozone production.

The expansion valve 16 is designed to drop the air pressure from, forexample, approximately 60 lbs. per sq. inch to 8 to 10 lbs. per sq. in.,thus producing the desired adiabatic cooling of the air as it enters theozone generator 10. The generator may be of the plate, wire grid orglass tube constructions, with the negative generator plates thereofbeing grounded for safety purposes. The generator may be charged by atransformer at a rating of 4000 to 5000 volts, 20 ma from the secondarycoil, one end of which is grounded to the common mounting plate of thegenerator. The timer circuit 19 is set to turn on the ozone generatingsystem intermittently, for example for 15 to 30 minutes each hour.

In use, and assuming that the system is full so that the level L of theliquid in the tanks 25 and 40, and in the ozonating tanks 71 to 75, isequal, then any additional fluid entering tank 25 will cause acorresponding amount to be discharged from the outlet 90 to the leachfield. Under these circumstances, water or effluent entering the filtertank 42 from tank 25 passes upwardly through the filter 44 and overflowsthrough the check or flap valve 67 to the upper end of tank 71. Asillustrated diagrammatically in FIG. 4, any fluid entering the upper endof tank 71 must flow downwardly in the tank against the flow of anyozone gas which may be discharged from time to time from the diffuser 77positioned adjacent the lower end of tank 71. The same fluid must thenpass through pipe 81, and upwardly through tank 72, and then throughpipe 82 and downwardly through tank 73. The fluid continues through pipe84 and upwardly in tank 74 and through pipe 85 and then downwardlythrough tank 75 and finally upwardly through pipe 86 into the reservoirdefined by the remaining space in tank 40 around the outside of filtertank 42. Any excess filtered liquid will be discharged through theoutlet 90.

During this time, periodic operation of the ozone generator 10 willcause ozone gas to be fed through pipe 20 to the bottoms of theozonating tanks 71 to 75. As this gas bubbles upwardly through thefiltered fluid in these tanks, it operates in known manner to killvarious forms of undesirable bacteria, and also increases the amount ofdissolved oxygen in the fluid. Excess ozone gas, air and foam, if any,are free to pass out of the openings formed in the upper ends of thetanks 71 to 75 above the liquid level L, and through the pipes 91, 92,93, 94 and 95 to the diffuser 96 in the septic tank 25.

After repeated operation, the pores of the filter 44 tend to becomeclogged. To correct this matter, conventional control means can beemployed to energize the pump 60 to effect backwash of the filter, bydrawing fluid through the inlet 61 of the pump, and pumping this fluidback through the pipe 63 to the septic tank 29. During this operationthe level of the liquid in tank 42, will drop rapidly; and in order toprovide enough clean water or fluid to backwash the filter, a siphonhose 101 (FIGS. 2 and 3) is supported by a bracket 102 from the tank 74so that one end of the hose communicates with the reservoir around theoutside of the tank 42, and the opposite end with tank 42 above thefilter 44. Thus, during a backwash operation, when the level of theliquid in the reservoir falls below the outer or upper end of the hose101, as shown in FIG. 2, the siphon or vacuum created in the hose 101will terminate, and this phenomenon can be utilized automatically, ifdesired, to shut off the pump 60 in any known manner.

If the filter 44 becomes excessively dirty or in need of replacement orservice, it can be withdrawn by its handle 52 from within the tank 42upon removal of the lid or cover 43 from the outer tank 40.

Referring now to FIG. 5, wherein like numerals are employed to denoteelements similar to those employed in the embodiment illustrated inFIGS. 1 to 4, the tanks 71 to 75 are designed so that the fluidtravelling therethrough must travel downwardly in each tank and thenupwardly through the inlet of the next tank. Tank 71, for example,contains a vertical riser pipe 111, the lower end of which opens on theinterior of tank 71 beneath the ozone diffuser 77, and the upper end ofwhich is connected to a horizontally disposed pipe 112, which ispositioned to register with the desired level L of the fluid in thetanks. Pipe 112 is connected to the upper end of the next ozonating tank72 in the series thereof; and tank 72 likewise contains a riser pipe113, which opens at its lower end adjacent the bottom of tank 72, andwhich is connected at its upper end through a horizontally disposedoutlet pipe 114 with the upper end of the next tank 73. Similarly, tanks73, 74, and 75 contain riser pipes 115, 117 and 119, respectively, whichare connected at their upper ends to outlet pipes 116, 118 and 120respectively. Pipe 116 is connected to the upper end of tank 74; pipe118 is connected to the upper end of tank 75; and pipe 120 opens on thereservoir located in tank 40 around the outside of the filter tank 42 inthe same manner as in the first embodiment. With the apparatusillustrated in FIG. 5, there is a counterflow of the fluid relative toany ozone gas diffused into the five ozonating tanks 71 to 75.

In the above-described apparatus the tank 40 may be made from, forexample, Fiberglas or the like, and the tubular or cylindrical ozonatingtanks 71 to 75 can be made, if desired, from a polyvinyl chloridematerial. Although the addition of a coagulant and polyelectrolyte tothe wastewater before entry to the septic tank 25 will reduce thesettling time for solids, it has been found that these supplements arenecessary only where the septic tank is not quite large enough to handlethe quantity of effluent it receives from the associated household.

In one installation of the above-noted apparatus, the filter housing 45contained a six inch layer 48 of peat gravel, covered by a three inchlayer 49 of anthrofil, and a three inch layer 50 of washed sand. Duringoperation of the pump 60 for backwash purposes, approximately 50 gallonsof water were drawn by the pump downwardly for approximately a tenminute interval, the additional water needed being drawn from thesurrounding reservoir by the siphon hose 101. This backwash operationcan be performed automatically and periodically, if desired, for exampleby use of a timer which intermittently operates the pump 60 in any knownmanner.

The excess ozone gas and air which is conveyed by the pipe 95 back tothe septic tank 25 activates the aerobic bacteria, and the excess ozonegas diffused out of pipe 96 oxidizes the suspended solids in the septictank. This operation produces a preozonation phase, and increases therate of settling, and the actions of the aerobic bacteria, and theanerobic bacteria at the bottom of the septic tank.

As shown in FIG. 2, the excess ozone and air which accumulates at thetop of tank 25 can be fed by a pipe 135 back to the top of tank 40 abovethe level of the liquid in the reservoir section of the tank, so that itcan pass out of the pipe 90 and be fed to the leaching field where itincreases the action of the anerobic bacteria and soil bacteria to helpkeep the field clean and unclogged.

Some researchers claim that the bacteria in the soil around the leachfield pipes cause poor circulation, while others claim that it is thesolids that pass from the septic tanks into the leach field that causeclogging. Still others claim that a coating of ferric sulphide on theinside of the pipes and soil around the pipes tend to block the pores inthe field. With applicant's above-noted system, however, the solids areremoved, the E coli are reduced to zero, upwards of 97% of the virus arekilled, odors and colors are eliminated from the effluent, and sulphidesare removed and sulphates are reduced to minimum levels, as are nitratesand turbidity. As a result, a clear, liquid effluent is allowed to flowthrough pipe 90 into the leach field.

One of the reasons for employing a plurality of diffusion tanks 71 to 75is to reduce the height of the system. For example, it has beendiscovered that, when fluid in a gravity-feed system flows in an ozoneatmosphere for height of approximately 16 feet, approximately 95% of theozone gas which is diffused into a liquid will be absorbed, and thedissolved oxygen level thereof will reach 10 ppm and higher, which isvery desireable level. However, to avoid the necessity of using a single16 foot high tank, a plurality of shorter tanks are used, and theeffluent is fed sucessively through the tanks so that it will travel adistance approximately equivalent to at least 16 feet before beingdischarged into the reservoir in tank 40. This provides a maximumcontact time with the ozone gas, and results in a more complete kill ofbacteria, oxidation of the dissolved organics, aeration by stripping ofammonia, and increases dissolved oxygen in the effluent.

Even better results can be achieved by using granulated activated carbon(charcoal) in one or more sections of the contact chamber, for exampleby placing the carbon in a removable receptacle placed on or adjacentthe bottom of the last tank 75 so that fluid will have to pass throughthe charcoal before entering line 86 or 119. This will remove ammonia,nitrates and materials oxidized by ozone, and will thus make the watersuitable for reuse for many purposes. Also the container can be replacedor replenished when the charcoal has become exhausted.

It has been discovered also that more rapid breakdown of solid particlesin the septic tank, and a reduction of undesirable sludge build-up inthe system, can be achieved by adding to the waste water entering theseptic tank small quantities (e.g. 0.5 ml. per liter of wast) ofdimethyl sulfoxide (DM SO). This can be done, for example, by mixing theDm SO with the coagulant for addition of the sewage through pipe 39. TheDM SO facilitates entry of the coagulant and anaerobic and aerobicbacteria into the solids which settle to the bottom of tank 25 therebyspeeding up approximately tenfold the breakdown of these solids.

If required by building or space conditions the effluent from the septictank may run into a sump in which a float controlled sump pump will pumpthe effluent from the sump to the tanks as described, which may beplaced above ground in some appropriate location. The excess liquid willthen flow by gravity from the last opening in the reservoir in the tankthrough a pipe connecting it to the leach field.

The clean effluent discharged from pipe 90 may be used for differentpurposes, rather than being leached into a field. For example, by usinga separate piping system connected to outlet 90 (not illustrated) thecleaned effluent could be used for irrigational purposes, or reused fortoilet use in the home, lawn, sprinkling, or possibly could be pipedinto a grade "A" stream or lake. Because the cleaned effluent containsno solids, it requires a smaller leach field than the ordinary septictank system. The system may employ a septic field in which the clearwater effluent is evaporated upwardly through a sand bed and topsoil asdeveloped, for example, by A. P. Bernhart of the University of Toronto,and known as the evapotransporation system.

While the invention disclosed herein has been described in detail inconnection with only certain embodiments thereof, it will be apparentthat it is capable of further modification, and that this application isintended to cover any such modification as may fall within the scope ofone skilled in the art or the appended claims.

Having thus described my invention, what I claim is:
 1. A method ofpurifying septic tank effluent flowing at substantially atmosphericpressure, comprisingpassing liquid effluent by gravity from a septictank successively through a plurality of serially-connected tanks, thefirst of which tanks in said series contains a filter for mechanicallyfiltering solids from the liquid as it passes through said first tank,intermittently feeding ozone gas through each of the remainder of saidserially-connected tanks during the passage of said liquid through saidremaining tanks, collecting the ozonated liquid in a reservoir afterpassage thereof through the last of said serially-connected tanks,allowing the ozonated liquid to flow by gravity out of said reservoirfrom an opening adjacent the upper end thereof, conveying excess ozonegas from said remaining tanks to said septic tank, and periodicallybackwashing said filter by reversing the flow of liquid through saidfirst tank and the filter therein, and returning the backwash liquid tosaid septic tank, said backwashing step including using at least someliquid from said reservoir for backwashing said filter.
 2. A method asdefined in claim 1, including passing said liquid through a layer ofgranulated activated carbon during its passage through one of saidremainder of said serially-connected tanks.
 3. A method as defined inclaim 1, including feeding said ozone gas in one direction through saidremaining tanks, and said liquid in the opposite direction.
 4. A methodas defined in claim 1, including feeding said ozone gas and said liquidin the same direction through said remaining tanks.
 5. A method asdefined in claim 1, wherein said liquid passes through said remainingtanks and in contact with said ozone gas for upwardly of approximatelyat least sixteen feet.
 6. A method of purifying septic tank effluent,comprisingfiltering the liquid effluent from a septic tank through aporous filter element, passing the filtered fluid by gravitysuccessively through a series of vertically disposed ozonating tanks,and for an overall distance of at least sixteen feet, intermittentlysupplying ozone gas to each of said ozonating tanks adjacent the lowerends thereof, conveying excess ozone gas from the upper ends of saidozonating tanks back to the associated septic tank to preozonate theliquid therein before it is filtered through said porous filter element,accumulating the filtered and ozonated liquid in a reservoir after itsdischarge from the last ozonating tank in said series thereof, andallowing said liquid to overflow from said reservoir, and at atmosphericpressure, into a leach field surrounding said reservoir.
 7. A method asdefined in claim 6, including passing said liquid through an activatedcharcoal filter before it passes from said last ozonating tank to saidreservoir.
 8. A method as defined in claim 6, including periodicallypumping said filtered liquid, and at least some liquid from saidreservoir, backwardly through said porous filter to said septic tank tobackwash said filter.